Vehicles equipped with inflatable restraints ("airbags") located in the bowl of a steering wheel utilize an electrically-actuated inflation device ("inflator") for deployment of the airbag in the event of a severe crash. Detection of a deployment crash conditions may be accomplished by a variety of means including conventional ball and tube inertial sensors, piezoelectric accelerometers or other varieties of known accelerometers. If a crash is determined by the controller to meet predetermined deployment conditions, an appropriate firing signal is output to the inflator which initiates deployment by sending current through a squib which in turn ignites a solid propellant.
Transfer of the deployment current to the inflator requires a means of electrical connection from a vehicle side wiring harness up the steering column an to the inflator. Typically, this electrical connection has been accomplished by means of a clockspring-type conductor allowing for full stop-to-stop steering wheel rotation while maintaining continuous electrical connectivity with the inflator.
A typical prior art clockspring-type conductor comprises a stationary outer housing coupled to the steering column, an inner housing rotatably supported by the outer housing and drivingly coupled to the steering shaft, and an electrical conductor supported by the stationary housing and loosely wound a plurality of turns around the inner housing. The conductor has one end connected via an electrical connector with the airbag controller via the vehicle side wiring harness, and its other end connected via an electrical connector with the inflator at the steering wheel. When the steering wheel is rotated in one direction, the conductor is wound tighter toward the inner housing and when rotated in the other direction, the conductor is loosened and unwound away from the inner housing.
To facilitate the addition of steering pad controls for controlling such vehicle systems as the radio, horn, windshield wipers, lights, heater and air conditioner, the device can incorporate multiple conductors. Alternative data communication interfaces of steering wheel controls includes optical couplers and slip ring configurations.
Although clockspring-type devices are satisfactory in electrical operation, they have certain mechanical shortcomings, for example: (i) incorrect installation during assembly or service of a steering system can result in the conductor cable being wound too tight, not allowing enough slack for full rotation of the steering wheel and causing damage to the connector if full rotation occurs, and (ii) clearances between the inner and outer housings necessary to permit rotation of the housings with respect to one another can result in a rattling or squeaking noise over bumpy roads or during rotation of the steering wheel.
Attempts to lock the inner and outer housings in position to prevent over-tightening of the connector cable during assembly or service of the steering system have included the use of an anti-rotation pin which is removed upon completion of the assembly. This, however, adds to the overall cost of the system, and complexity of its installation.
There is a desire to provide an apparatus for transferring power and communication data across the annular gap defined by a steering column and steering shaft without the need for any direct electrical connection, thereby overcoming the shortcomings of the prior art clockspring-type devices.
It has been proposed to couple a firing pulse current to an airbag inflator by rotary transformer action. However, the energy requirements of an inflator may preclude practical application of this concept due to size, mass and packaging concerns associated with a suitable transformer capable of developing the required energy with appropriate expediency.